1. Field of the Invention
The subject invention is related to high definition television and to a system for transmitting high definition television signals over standard terrestrial and cable television transmission channels.
2. Description of Related Art
Color television signals are currently being transmitted to consumers in accordance with one of several television transmission standards, for example, NTSC and PAL. These standards prescribe various characteristics of the transmission signal, i.e., 525 or 625 scanning lines presented in two consecutive, interlaced fields forming each picture frame at a field rate of 60 (or more precisely 59.94) or 50 Hz, to be transmitted over a transmission channel having a bandwidth of at most 6 MHz.
Over the last few years, there has been increased interest in improving the quality of the received television picture. One of these areas is improving the horizontal and vertical resolution of the television signal. Another area is to change the aspect ratio from a standard ratio of 4:3 to a wide-screen ratio of 16:9. A benefit of this wide-screen ratio is that it is substantially similar to the aspect ratio used in preparing motion plctures. Therefore it would no longer be necessary to clip side portions of the picture in order to present the same on television. Another of these areas is an improvement in the quality of the audio signal accompanying the transmission.
A common problem in each of the above areas of improvement is that, without special encoding, bandwidth in excess of the above prescribed 6 MHz is required. This, in turn, raises another problem.
In the United States, for example, there is a substantial universe of NTSC television receivers. If one were to look back in time to the advent of color television, one should note that in deference to the universe of black-and-white televisions, the Federal Communications Commission (FCC) ruled that any color television signal transmission must be compatible with these black-and-white television receivers.
This same stance is being taken by the FCC with respect to HDTV transmissions, i.e., they must be compatible with the universe of existing NTSC television receivers. In this instance, compatibility means that a standard television, while not being able to display an HDTV picture, may nonetheless be capable of showing a standard display using the same transmission.